I love questions like this, partly because I really hate them.
On top of "how do you define great? ", there's the "do you mean historically, this decade, or last year?".
Since somebody already jumped on the Meyer grenade, I'll put Spurrier into the mix. No man in the history of the NCAA has ever gotten away with so much trash-talking in the name of School Spirit without giving the NCAA a legitimate excuse to censure him.
He's gone down-hill since he left Florida, but I don't think you can talk about great coaching in the 20th Century without mentioning Spurrier's 1996 poster-show, where he tracked the Vols from pre-season to post-season-- from possible National Champions, to, thanks to Memphis, Knox County Champions...
Somebody come up with a "What you talkin' 'bout Lewis" scale for what we're supposed to mean by "Best" CF football coach. If we're going to argue about something, we might as well get back to basics.